Wheel bearing apparatus to support a vehicle wheel is an apparatus to rotatably support a wheel mounting wheel hub, via double row rolling bearings, for driving wheels and driven wheels. For structural reasons, in general, a bearing of an inner ring rotation type is used for driving wheels. Both inner ring rotation and outer ring rotation types are used for driven wheels. In general, the wheel bearing apparatus is classified into a so-called first-generation type where the wheel bearing includes double row angular ball bearings fit between a knuckle and a wheel hub. A second-generation type is where the body mounting flange or the wheel mounting flange is directly formed on the outer circumferential surface of the outer member. A third generation type is where one of inner raceway surfaces is formed directly on the outer circumferential surface of the wheel hub. A fourth generation type is where an inner raceway surface is formed directly on the outer circumferential surface of the outer joint member of the wheel hub and the constant velocity universal joint, respectively.
In the bearing portion of these wheel bearing apparatus, seals are provided to prevent leakage of grease contained within the bearing as well as to prevent ingress of rain water or dust into the bearing. Recently, the automobile industry has moved toward maintenance-free bearings and thus requires the bearing to have a longer life. Investigation into the cause of damages to the bearing has yielded that a substantial part of the cause of damage is due to trouble with the seal of the bearing rather than the primary cause such as delamination of the bearing surface. Accordingly, the life of a bearing apparatus can be improved by improving the sealability and durability of the bearing apparatus.
Various seals for wheel bearing apparatus have been proposed, one example is shown in FIG. 15. This wheel bearing apparatus is of a so-called third generation type for a driven wheel. It includes an outer member 101 integrally formed on its outer circumferential surface with a body mounting flange 101b, to be mounted on a knuckle (not shown) of a vehicle. Its inner circumferential surface is formed with double row outer raceway surfaces (101a, 101a). An inner member, including a wheel hub 103, has a wheel mounting flange 102 integrally formed at one end. One 103a of double row inner raceway surfaces (103a, 104a) is arranged opposite to the double row outer raceway surfaces (101a, 101a). A cylindrical portion 103b axially extends from the inner raceway surface 103a. A threaded portion 103c is formed on the end of the cylindrical portion 103b. An inner ring is fit onto the cylindrical portion 103b of the wheel hub 103. Its outer circumferential surface is formed with the other one 104a of double row inner raceway surfaces (103a, 104a). Double row rolling elements (balls) 107, 107 are rollably arranged between the outer and inner raceway surfaces, via cages 106.
Hub bolts 102a are mounted on the wheel mounting flange 102 equidistantly apart from each other along the periphery. A securing nut 108 is fastened to the end of the wheel hub 103 to axially immovably secure the inner ring 104 relative to the wheel hub 103. In addition, a seal 109 is mounted between the outer-side end of the outer member 101 and the wheel hub 103. A cap (not shown) is mounted on the inner-side end of the outer member 101 to prevent leakage of grease contained within the bearing, as well as ingress of rain water or dust into the bearing.
As shown in an enlarged view in FIG. 16, the seal 109 has a metal core 110 and a sealing member 111 integrated with the metal core 110 by vulcanized adhesion. The metal core 110 has a cylindrical press fitting portion 112 to be fit into the outer member 101. An inner portion 113 of the metal core 110 is bent at the axially inner end of the press fitting portion 112 to extend radially inward from it. An outer portion 114 extends upward from the axially outer end of the press fitting portion 112. The outer portion 114 is arranged to be in contact with the outer-side end of the outer member 101.
The sealing member 111 is formed of an elastic material such as synthetic resin. The sealing member 111 is adhered to the metal core 110 over a range from a portion of the outer-side surface of the outer portion 114 of the metal core 110 to a tip of the inner portion 113 of the metal core 110. The sealing member 111 further extends to the inner-side surface of the inner portion 113 and surrounds the tip.
The sealing member 111 is provided with two side lips 115, 116. The lips 115, 116 are inclined and extend radially outward to contact a surface of the base of the wheel mounting flange 102 when the seal 109 is assembled on the bearing apparatus. In addition, a radial lip 117 is arranged at the tip of the inner portion 113 of the metal core 110. The tip 117 is bent to contact with a round corner portion 118 at the base of the wheel mounting flange 102 when the seal 109 is assembled on the wheel bearing apparatus.
In such a structure of the seal 109, the rain water or dust coming into the wheel bearing apparatus will flow or be gathered in a groove formed by the radially outermost side lip 115 and flow downward. The radially inner side lip 116 can prevent slight rain water or dust which would passed through the radially outermost side lip 115 from entering into the bearing. In addition the radial lip 117 can prevent grease contained in the bearing from flowing out from the bearing. Although there would be variation in axial interference of the sealing member 111 against the wheel hub 103, the two side lips 115, 116 will exhibit high sealing performance due to their flexible deformation. The seal 109 is also designed in a compact and slim configuration so as to be adapted to a small space near the rounded portion 118 of the base of the wheel mounting flange 102. A Reference patent document is Japanese Laid-open Utility model Publication No. 34224/1995
The seal 109 of the prior art wheel bearing apparatus has a groove feature on its outer circumferential surface which rain water or dust gather and flow downward to be discharged from the seal 109. Sometimes a problem occurs in that muddy water enters into the narrow space between the wheel hub 103 and the outer member 101. The muddy water solidifies after it dries and thus flexible deformation of the side lip 115 is prevented. If the flexible deformation of the side lip 115 is suppressed, wear of the side lip 115 is accelerated by dust or sand adhered to the tip of the lip 115. Thus, the sealability of the seal 109 is spoiled. In addition, since the end surface of the outer member 101 and the outer portion 114 of the metal core 110 directly contacts with each other, via metal-to-metal contact, corrosion is accelerated by rain water entering therebetween and thus the sealability is also spoiled.